Earlier quoted context omitted.
We do in fact have another billionaire, Yuri Millner, to push humanity towards the goal of reaching other stars with his "Breakthrough Starshot" initiative.
As far as I know this would be cell phone sized with no way of slowing down. It would cross entire solar systems within a few hours.
There's no way to slow down, true.
Let's see... Neptune's orbital diameter 8.3 light hours.
At 10% c (speed of light) you would need 83 hours. Yes, insane speed, yet hopefully enough time to take quite a few pictures.
Also the plan is not to send a single "disc", but many (thousands?). Together they could potentially provide a treasure trove of data from within the alien solar system.